Structural polymers such as plastic materials are used in numerous and diverse applications. In fact, those skilled in the art continue to strive to replace parts conventionally made from metal and wood with those made from polymers. The polymers, for instance, may offer various advantages with respect to strength properties, chemical resistance, and/or cost.
One problem that has been encountered in producing molded polymer articles, however, is the ability to produce articles with a distinctive look or appearance. For instance, molded polymer articles are generally uniform in color. In certain applications, however, multi-colored parts are desired. Thus, in the past, non-dispersing pigments or pigment particles have been incorporated into polymers in order to produce articles having contrasting colors. Such non-dispersing pigments, for instance, have been used to produce speckled surfaces or parts having a tortoise-like appearance. Processes for producing molded articles having contrasting color properties are disclosed, for instance, in European Patent Application No. EP 0931807, International PCT Application Publication No. WO 97/37825, U.S. Pat. Nos. 4,125,582, 4,183,673, 5,053,176, 5,489,656, and U.S. Patent Application Publication No. 2001/0045680, which are all incorporated herein by reference.
When attempting to produce molded polymer articles having multiple colors, however, problems have been experienced in producing articles with the desired effect without adversely impacting other properties of the polymer. For instance, producing polymer articles with multiple colors can adversely impact upon the strength of the resulting material depending upon the mixture of materials that are used to produce the part.
One particular type of structural polymer that has good rigidity and strength properties are polyoxymethylene polymers. Polyoxymethylene (which is also referred to as “POM”) is a high-performance polymer having good mechanical properties. Due to its properties, polyoxymethylene polymers are commonly used as a direct replacement for metals due to its stiffness, dimensional stability, and corrosion resistance. Polyoxymethylene polymers exist in the form of homopolymers and copolymers.
Although polyoxymethylene polymers have a desirable combination of physical properties, various problems have been encountered in attempting to produce multi-colored articles containing a polyoxymethylene polymer. In particular, the problems described above have been particularly problematic when processing polyoxymethylene polymers. Thus, a need currently exists for a polymer composition and method capable of producing multi-colored articles from polyoxymethylene polymers.